This invention relates to electric motor construction, and more particularly subfractional horsepower alternating current motors. Many such motors are constructed with two bearings in the frame or stator for journaling the rotor shaft near each end thereof. The present invention is concerned with a single or unit bearing motor wherein there is only one fixed bearing which journals a single journal portion on the rotor shaft. Motors of this type are shown in U.S. Pat. Nos. 3,293,729 and 4,045,698. Different methods have been proposed for assembling these small motors, and the former patent suggested an assembly method which included forming a laminated pole piece member of at least two superposed, thin laminations. U.S. Pat. No. 3,165,816 showed motors with two bearings, and also showed a motor with a single bearing. In that single bearing motor, it was proposed to use shims to space the rotor and stator, and then to use a settable adhesive to hold the bearings in alignment. U.S. Pat. No. 3,755,889 showed another unit bearing motor wherein a plurality of shims between the rotor and stator were used for alignment.
In the typical motor with two bearings, it is common in the smaller sizes of motors to have the rotor laminations with an aperture therein just the size of the shaft and to be secured directly to the shaft. In a unit bearing motor, in order to avoid a long overhang of the mounting of the rotor, it has been common to utilize a hollow sleeve-type of hub, with the hub secured at one end to the shaft and a large diameter portion of the hub carrying the stack of rotor laminations. Then a fixed bearing may extend inside the rotatable sleeve portion of the hub and be a bearing for a journal portion on the shaft so that the journal portion of the shaft longitudinally is substantially centered in the lamination stack. This eliminates the long overhang of the center of gravity of the rotor relative to the journal portion of the unit bearing. However, this means that the rotor laminations must have a large diameter aperture therein for mounting on this sleeve portion of the enlarged hub. It also introduces another manufactured item, the hub, with its attendant tolerances of inside diameter receiving the shaft and outside diameter receiving the lamination stack. This increases the chances of eccentricity of the rotor relative to the stator and, accordingly, the air gap must be made large enough to take care of such potential eccentricity in a series of manufactured motors.
For many years, an assembly method used in unit bearing motors has been to assemble the shaft with an aluminum hub, and then to machine the hub to be concentric with the shaft within a satisfactory limit. Next, the stack of rotor laminations which formed the core was die-cast separately to have mounted therein the squirrel-cage winding. This subassembly was then pressed onto the machined hub. Next, the outside diameter of the rotor lamination stack was ground to be concentric with the shaft within satisfactory limits.
A second method of assembling unit bearing motors has been practiced for a number of years, and this included extruding an aluminum or brass hub and then stacking the rotor laminations on this hub. This hub and lamination stack was then placed in a die casting machine and the squirrel cage winding die-cast onto the lamination stack. As a part of this die casting, a core pin had to be used to close the central aperture in the hub which would later receive the shaft. Next, after removal from the die casting machine, a fluted shaft was pressed into the aluminum or brass hub and secured, for example, by some anaerobic adhesive. Then, the outer diameter of the lamination stack was turned to be concentric with the shaft within satisfactory concentricity limits.
In both of these two prior art methods of rotor assembly, a number of steps were required. In the first of the two methods mentioned above, the assembly method was too labor-intensive and consisted of too many steps to be adequately competitive in the present marketplace. In the second of the two above-described methods, it was quite difficult to obtain adequate concentricity because of the imprecision of the press-fit of the shaft with flutes thereon into the small aperture of the hub. Also, with the squirrel-cage die casting being performed prior to the shaft being in place in the hub, there was no extra rigidity imparted to the entire rotor assembly by the die casting, and it was typical to have 0.003 inch eccentricity of the rotor O.D of 1.5 to 2 inches, for example. Because of this large eccentricity compared with the size of the motor, it was typical to have an air gap between the rotor and stator of 0.012 inch to make certain that the rotor would not rub on the stator, especially if the bearing started to wear. Actually, the bearing did wear out much more quickly because of the dynamic unbalance due to the eccentricity of the rotor.
The General Electric Company has had a long history of unit bearing motors since the U.S. Pat. No. 526,686 to Clark of 1894. This showed a rotating shaft in a commutator-type motor. The Morrill U.S. Pat. No. 2,306,743 showed an induction-type motor with a unit bearing but with some cantilever overhang on the rotor relative to the unit bearing. The Bradley U.S. Pat. No. 2,522,985, filed Dec. 29, 1945, also showed an induction motor, again with some overhang of the rotor relative to the unit bearing and with the squirrel cage cast onto a separate sleeve which was splined to the rotating shaft. This is generally the construction used on small unit bearing motors by General Electric in production to this day.
The Bradley U.S. Pat. No. 2,571,672 followed the design of the previous patent but extended the unit bearing deeper into the rotor so that there was less cantilever overhang relative to the bearing. The Feiertag U.S. Pat. No. 2,685,658 was another suggested General Electric design of a unit bearing motor but again had considerable overhang of the rotor relative to the unit bearing. The Dochterman U.S. Pat. No. 2,782,720 and the reissue 24,909 thereof showed a unit bearing motor in a fixed shaft configuration. The Thompson et al. U.S. Pat. No. 3,165,816 showed two-bearing motors and also a unit bearing motor in FIG. 11 again with the squirrel cage cast onto a separate sleeve splined to the shaft. The Dochterman U.S. Pat. No. 3,420,335 again showed the typical General Electric construction of the squirrel cage cast onto a sleeve splined to the rotating shaft. The Busian U.S. Pat. No. 3,755,889 showed a unit bearing motor but gave no details of the rotor construction, that invention being directed to assembling by use of shims. The Dochterman U.S. Pat. No. 3,874,073, similar to Busian, did not show the details of the rotor construction. Instead, the invention was directed to removing heat from the stator. The Uhen U.S. Pat. No. 4,565,937 again showed the typical General Electric construction of the squirrel cage cast onto a sleeve which was splined to the rotating shaft of a unit bearing motor.
Others of the prior art have suggested unit bearing motors, and these include the Else U.S. Pat. No. 253,425 assigned to Westinghouse Electric & Manufacturing Company. This patent suggested a construction of oil flow along the shaft and return to a reservoir. The Levy et al. U.S. Pat. No. 2,067,155 assigned to General Motors Corporation showed a unit bearing induction motor with the squirrel cage extended to drive a fan. The Gillen U.S. Pat. No. 2,501,814 showed a fixed shaft unit bearing motor with the output rotatable shaft connected to the rotor squirrel cage by a dome-shaped element. The Gillen U.S. Pat. No. 2,522,941 again showed a fixed shaft motor of the inside out construction. The Lautner U.S. Pat. No. 2,659,831, assigned to Knapp Monarch Company, showed a unit bearing motor with a considerable overhang of the rotor relative to the bearing. The Lautner U.S. Pat. No. 2,904,709, assigned to Howard Industries, Inc., showed a fixed shaft unit bearing motor. The Ernst U.S. Pat. No. 3,111,743 showed a fixed shaft motor with the output rotatable shaft connected to the squirrel cage conductor bars by a dome-shaped element. The Morrill U.S. Pat. No. 3,293,729 showed the rotor laminations mounted on a hub secured to the shaft. The Morrill U.S. Pat. No. 4,045,698 also showed the rotor laminations mounted on a hub secured to the shaft. The Peachee, Jr., U.S. Pat. No. 4,209,722 showed a unit bearing motor with the squirrel cage die cast onto a sleeve which was splined to the shaft. The Davis U.S. Pat. No. 4,430,590 showed a unit bearing motor with a fixed shaft. The Peachee, Jr., U.S. Pat. No. 4,499,661 showed a unit bearing motor with the squirrel cage and rotor laminations mounted on a hub which was splined to the shaft. These patents all showed constructions which were labor-intensive, which makes the motors costly to produce.